The prices of high-speed storage devices are becoming lower, and a large-capacity memory or a solid state disk (SSD) may be adopted in some cases for a host computer (hereinafter, operation host) that carries out operations (for example, database management).
Further, a known technique for storage systems involves temporarily caching data in a storage device having a high access rate to thereby speed up a response to a host computer. A known technique concerning a cache involves, for example, directly using, in a clustered storage, an update value and a value before the update of data held in a cache memory of each cluster through a network that couples the clusters to one another, to thereby avoid a decrease in use efficiency of the cache memories (see Patent Literature 1).
Another known technique involves ensuring data consistency of a plurality of storage volumes when a plurality of replicas are created for storage volume data in a storage apparatus (see Patent Literature 2).